Blood plasma contains several proteins that exhibit insulin-like effects when studied in isolated tissue systems; to date, these have been identified as pancreatic insulin and proinsulin, somatomedin and a larger molecular weight protein, the biologic significance of which remains controversial. This large molecular weight insulin-like serum protein is presently termed "nonsuppressible" because insulin antiserum fails to inhibit its biologic effects in isolated tissue systems. Nonsuppressible insulin-like activity (NSILA) comprises 70 to 90% of the total serum insulin-like activity. We have purified the serum protein largely responsible for serum NSILA and have developed a specific antiserum in rabbits. We now propose to investigate its biological role. The broad objectives of this project are to 1) elucidate the chemical and biological relationships of NSILA to insulin, 2) determine the endocrine control mechanisms influencing NSILA levels, and 3) define the role of NSILA in tissue repair processes. The relationship of NSILA to insulin will be studied by (a) further characterizing the physicochemical nature of purified NSILA, (b) development of a double antibody immunoassay to NSILA and subsequent determination of normal levels in animals and man, its metabolic clearance rate and its relationship to total insulin secretion following oral glucose challenge, and (c) characterization of cell membrane receptor interactions between NSILA and insulin in various target tissues. Endocrine control mechanisms will be studied by determining immunoreactive NSILA levels following various endocrine ablative and hormone replacement procedures. Finally, the role of NSILA in tissues repair processes will be studied in vivo and in vitro. In vivo studies will employ models of wound healing in the rat, correlating serum NSILA levels with wound repair. In vitro stdies will employ tissue culture methods, assessing the affect of NSILA levels in the added serum on fibroblast doubling times, collagen and glycosaminoglycan biosynthesis.